The application generally relates to an apparatus and method for feeding pulverized coal into a blast furnace through a pulverized coal injection lance. The application relates more specifically to a pulverized coal injection lance for controlling the swirl parameter of a gas flow to vary dispersion of coal particles injected through the injection lance, and a method for varying the dispersion of coal particles injected using the injection lance.
In metallurgical ore smelting operations, fuel and combustion gases may be supplied to a blast furnace through injection lances that end in tuyeres, which deliver a blast of air into a blast furnace. Pulverized coal injection lances are generally used to inject pulverized coal as a substitute to coke into a blast furnace. Pulverized coal is conveyed pneumatically through the injection lance and fed into an oxidizing atmosphere in a tuyere, through which hot blast air is blown into the furnace. To ensure that the pulverized coal burns completely the combustion reaction should begin as close to the lance tip as possible. Oxycoal lances exist that consist of an inner pipe for conveying the pulverized coal and a concentric outer pipe for conveying combustive gas, generally pure oxygen.
It has been found, however, that the flame at the lance tip is not stable and does sporadically go out. In some cases, the flame can automatically reignite without intervention. This can however not be guaranteed. If the combustion of the pulverized coal does not take place at the lance tip because the flame has extinguished, the pulverized coal and the oxygen are fed into the blast furnace, and complete burning of the pulverized coal cannot be guaranteed.
A number of solutions have been proposed to improve the burning efficiency at the lance tip, generally by improving the mixing of the pulverized coal and oxygen. For example, EP 1060272 describes that the burning of the pulverized coal can be improved and the flame maintained by providing a flow swirler between the coaxial pipes so as to impart a swirling motion to the oxygen fed to the lance tip. The effect of the flow swirler depends on the structure of the lance. If the spiral angle is too deep, the oxygen is directed away from the pulverized coal and the burning efficiency is decreased. If the spiral angle is too shallow, the improvement of the burning efficiency is negligible. The swirl ratio is geometry dependent and hence constant for the flow swirler lance, particularly since there is only one feeder channel for the oxygen.
Another proposed solution is described in U.S. Published Patent Application No. 2011/0180978 provides a pulverized coal injection lance having an inner pipe for conveying pulverized coal and an outer pipe, coaxially arranged around the inner pipe, for conveying combustive gas. The inner pipe forms a separation wall that separates the pulverized coal from the combustive gas. The pulverized coal injection lance includes a lance tip arranged in the tuyere that allows pulverized coal and combustive gas to form a mixture of at the lance tip, while ensuring that the flame is maintained at the lance tip. The coaxial pipe coal injection lance does not provide any capability for imparting swirl into the fuel train, and therefore no means for varying a swirl ratio.
What is needed is an injection lance that provides a desired distribution of coal particles that may be varied. Different smelting plants may have different requirements relative to their specific geometries and furnace operating conditions. In each of these cases, it may be possible to obtain a similar distribution of particles by changing the proportion of the air that enters the ports, if there were multiple gas flow channels. It may also be possible to achieve a change in the maximum possible swirl ration by changing the exit angle of helical ports.
Intended advantages of the disclosed systems and/or methods satisfy one or more of these needs or provide other advantageous features. Other features and advantages will be made apparent from the present specification. The teachings disclosed extend to those embodiments that fall within the scope of the claims, regardless of whether they accomplish one or more of the aforementioned needs.